Download Lecture7 - UCSB Physics

Astronomy 1 – Fall 2016
Lecture 7: October 13, 2016
Previously on Astro 1
•  Properties of the Planets:
–  Orbits in the same plane and direction
–  Inner (terrestrial) planets are small and made of heavy elements
–  Outer (Jovian) planets are big and made of light elements
•  Other bodies in the Solar system
–  There are seven large satellites (like the moon)
–  Asteroids in Asteroid Belt between Mars and Jupiter
–  Outer solar system is populated by TNO and comets
•  How do we learn about solar system bodies?
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We send probes
Spectroscopy reveals the composition of atmospheres
Craters are erased by plate geological processes
Magnetic fields reveal the presence of a rotating liquid core
The Diversity of the Solar System
Results from Its Origin and Evolution
Today on Astro-1
What is the origin of the solar system?
When did it form?
What is it made of?
How did it come to be this way?
Do most stars have planetary systems?
Are exoplanet systems similar to our Solar System?
Are there exoplanets in the habitable zone of other
stars?
Meteorites: Rocks from Space
•  How do we know it came
from space?
Surface shows evidence of
having been melted by air
friction as it entered our
atmosphere at 40,000 km/h
(25,000 mi/h).
•  How old are these rocks?
The ratios of various nuclei,
a method called radioactive
age dating, are used to
determine the rocks formed
4.56 x 109 years ago.
When did the solar system form?
•  The age of the universe, 13.7 x 109 years, has been measured
from its expansion rate. •The universe reached two-thirds of its
present age before our solar system came into existence.
•  The Sun and Earth are nearly as old as meteorites, the oldest
objects in the solar system.
The Solar System is Mainly H and He
•  All elements heavier than
zinc (Zn) have
abundances of fewer than
1000 atoms per 1012
atoms of hydrogen.
•  All elements heavier than
Boron (atomic number 5)
were made inside stars.
•  This composition is
typical of the Universe as
a whole.
•  Why is the composition of
the Earth not very
representative of the solar
system?
Dust that used to
be in Antares
Antares
The dying
star Antares
is shedding
material from
its outer
layers,
forming a
thin cloud
around the
star.
Stars Lose Mass è Enrich Their
Environment with Heavier Elements
The dying star Antares is
shedding material from its
outer layers, forming a thin
cloud around the star.
Why is this nebula blue?
To understand the formation of the planets,
we need to look at the formation of the Sun.
Most of the mass of the solar system is in
the Sun.
The Sun’s composition is close to that of
the protostellar nebula.
Protostellar Disks: Planets Are
Likely Forming Here
High Resolution Images of a Dusty Disk
•  The bands are almost certainly the
result of planets forming in the disk.
•  Grain collisions create pebbles that
ultimately grow into larger bodies
called planetesimals (and planets).
Planets disrupt the disk creating the
rings.
•  Seen for first time! ALMA
delivered 0.035” (5 AU) resolution.
•  How could such high resolution be
achieved?
•  What part of EM spectrum?
Sub-mm Interferometry
Cool, but why are the young stars surrounded by disks?
Gravity Causes Interstellar Gas
Clouds to Collapse
Planets Form Out of Gas Disks
Conservation of Angular Momentum
Taking a Closer Look at a Stellar Nursery
Heat from the Hot Protosun Separated
the Solar Nebular into Two Regions
Inner Region: Only rocky and metallic materials remained solid
Outer Region: Icy frost condensed beyond the snowline providing
more mass for planet building.
Accretion of the Terrestrial Planets
Planetary Migration
Planetary Migration
The Kuiper Belt: The gravitational influence of the Jovian planets pushed
small, icy objects to the outer reaches of the solar system past Neptune. The
result shown in this artist’s conception is the Kuiper belt, a ring populated by
trans-Neptunian objects like Pluto, icy planetesimals, and dust.
Origin of the Chemical Elements
(iclicker Question)
How has the present mix of chemical elements in the
Universe been produced?
A) All the known elements have been formed by the
radioactive breakup of the heavy elements formed in the
initial Big Bang
B) All of the known elements were formed in the Big
Bang.
C) H and He were formed in the Big Bang, while the
heavier elements have been slowly forming by collisions
in cold interstellar gas clouds
D) H and some He were formed in the Big Bang, while
the heavier elements have been slowly formed in the
centers of stars over the life of the Universe.
E) All the known elements were formed inside stars.
How did the Earth form?
(iclickers Question)
• The formation of terrestrial planets around a star is thought
to have occurred by what process?
•  A) Breakup of a large disk of matter which formed
around the star
•  B) Condensation of gas from the original star nebula
•  C) Capture by the star of objects traversing the depths
of space
•  D) Accretion or slow accumulation of smaller particles
by mutual gravitational attraction
Insight from other worlds
Methods
Direct imaging
Radial velocity
Transit photometry (light curves)
Astrometric wobble
Direct Imaging Presents a Contrast Problem
Four Planets Orbit
the Star HR 8799
First Extrasolar Planet
Visible in a Telescope Image
The Wobble of 51 Pegasi
Detecting a Planet by Measuring
Its Parent Star’s Motion
Hot Jupiters!?
Many planets about the
size of Jupiter orbit closer
to their star than
Mercury does to our Sun!
Early studies subject to a
selection bias. Most
sensitive to short period
planets.
NASA’s Kepler Mission
Summary
Solar System Formation: the nebular hypothesis.
The Sun:
formed by gravitational contraction of the center of the nebula.
Terrestrial planets:
formed through accretion of dust particles into planetesimals,
then into larger protoplanets.
Jovian planets:
Began as rocky protoplanetary cores, similar in character to the
terrestrial planets. Gas then accreted onto these cores.
Alternatively, they formed directly from the gases of the solar
nebula. In this model the cores formed from planetesimals
falling into the planets.
Homework (Due Tuesday 10/18)
• 
• 
Do all review questions from chapter 8 on your own.
For TAs, do
•  8.46 – make measurements from image of disk
•  8.47 – find the mass of a star from the orbit of its planet
•  8.49 – compare the spectra from a planet and its star
•  8.50 – estimate distance between a star and its planet from
a picture then calculate the orbital period.
• 
Note: For Tuesday October 18th, please read chapter 10 “Our
Moon”.
First Midterm Next Thursday!
• 
You may use a calculator. Bring one. No devices that can
connect to the internet.
• 
Exam has 50 multiple choice questions.
•  You must bring a ParSCORE sheet.
•  Buy the version where you bubble in your NAME
AND PERM #; it is red.
•  Check with your TA that you bought the right kind.
•  You must bring a #2 pencil.
• 
Exam will include the equation sheet.
•  See example on course webpage.
•  Do not bring an equation sheet.
How Should You Study?
• 
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Go over the Key Ideas at the end of chapters 1-8.
Go over the Review Questions for ch. 1-8.
• 
Go over the homework solutions for ch. 1-8.
•  We only grade a subset of the problems.
•  You need to ‘check’ the solutions to the other problems
yourself.
•  Exam tests whether you understand the concepts and can
apply them.
• 
It is not intended to be about memorization.